1. Field of the Invention
The invention relates to an injector/nozzle needle combination, with a control chamber coupling, for injecting fuel which is at high pressure into the combustion chambers of a direct-injection internal combustion engine. In injectors that are used to inject fuel, which is at high pressure, into the combustion chambers of an internal combustion engine, fast closure of the nozzle needle is a goal, once the injection phase, either a preinjection phase or a main injection phase, has been concluded.
2. Prior Art
German Patent DE 37 28 817 C2 relates to a fuel injection pump for internal combustion engines. In the device of this German patent, a control valve member comprises a valve shaft, which forms a guide sleeve and slides in a conduit, and a valve head connected to it and oriented toward the actuating device.
Also in this device, the sealing face of the valve head is embodied to cooperate with the face, forming the valve seat, of the control bore. The valve shaft, on its circumference, has a recess whose axial length extends from the discharge opening of the fuel supply line to the beginning of the sealing face, cooperating with the valve seat, on the valve head. A face exposed to the pressure of the fuel supply line is embodied in the recess, and the surface area of this face is equal to a surface area of the valve head that in the closed state of the control valve is exposed to the pressure of the fuel supply line. As a result, it can be attained that the valve in the closed state is pressure-equalized, and hence the mechanical stresses on the control valve member known from DE 37 28 817 C2 are drastically reduced. Furthermore, a spring urging the control valve toward its open position is disposed in the guide sleeve already mentioned.
In this arrangement from the prior art, no provision for positive control of a nozzle needle whose inflow is effected via a control valve unit supported displaceably laterally in the injector housing is provided.
With the embodiment proposed according to this invention, a pressure-controlled injector assembly can be achieved whose nozzle needle can be positively controlled for closing and opening. By the opening or closing of the control chamber, provided in the upper region of the housing of the injector, a negative pressure, or an overpressure can be generated in a further control chamber inside the housing of the injector, which assists movement of the nozzle needle of the injector vertically up and down in its guide. The further control chamber is alternatively, by means of movement of a control part, in communication with either the leaking oil side or the high-pressure side. The pressure in the further control chamber is affected solely by the motion of the control part.
In an upward motion of the control part into its housing bore, outward motion of a face end of the control part, which represents a boundary of the further control chamber, causes a negative pressure in the further control chamber, and the opening of the nozzle needle out of its seat is reinforced. Along with the pressure shoulder embodied on the nozzle needle, on which pressure shoulder a pressure prevailing in the high-pressure collection chamber acts via the nozzle inlet, the nozzle needle opening is reinforced by the negative pressure generated in the further control chamber.
Conversely, in the case of closure of the nozzle needle by insertion of the face end of the control part into the further control chamber, the insertion motion of the nozzle needle into its seat is reinforced. This takes away the possibility of postinjections into the combustion chamber of a direct-injection internal combustion engine. With the possibility of positive control of the nozzle as proposed by the invention, via its pressure control, a precise conversion of a triangularly configured injection nozzle pressure can be established. Besides the action on the nozzle chamber and its relief via the leaking oil outlets, the injection nozzle can be urged, by the changes in pressure in the further control chamber in directions that reinforces the opening and closing events of the injection bore, so that an optimal triangular course of injection can ensue. To achieve an optimal, triangularly configured pressure course at the tip of the injection nozzle, it is extremely important for postinjections into the combustion chambers of a direct-injection internal combustion engine to be prevented by fast needle closure. The embodiment according to the invention, where the nozzle needle is acted upon via a further control chamber, is especially simple to accomplish from a production standpoint and makes a major contribution to this prevention of postinjections.